1. Field of the Invention
The present invention relates to a joint which is mounted on the end portion of a spiral pipe used for protection of a communication cable or a conductor cable or a spiral pipe used for transport of fluid, and is used to connect the spiral pipe to another spiral pipe or to the box body of a manhole. The present invention also relates a method of connecting a joint to a spiral pipe with an outer periphery of a pipe wall thereof formed in an uneven spiral shape.
2. Description of the Related Art
In related art, as shown in FIG. 13 which is a side surface section view of a spiral pipe joint when it is mounted on a spiral pipe, the spiral pipe joint includes a nipple 1a and a caulking ring 2a. The nipple 1a is to be inserted into the end portion of a pipe body P of the spiral pipe and provides a joint main body. The caulking ring 2a fixes the pipe body P to the nipple 1a. The nipple 1a includes a flange portion 12a, an inserting portion 11a, and a group of annular projections 13a. The flange portion 12a is formed of metal in substantially a cylindrical shape and is formed in the end portion of the nipple 1a. The inserting portion 11a is to be inserted into the pipe body P. Each of the group of annular projections 13a is disposed on the outer surface of the inserting portion 11a. The axial-direction section of the group of annular projections 13a is substantially a saw-tooth shape having an acute angle with respect to the end portion at opposite side of the flange portion 12a. On the other hand, the caulking ring 2a is formed of metal in a cylindrical shape and has a dimension, which allows the caulking ring 2a to be fitted with the outer peripheral surface of the pipe body P. Specifically, after the inserting portion 11a of the nipple 1a is inserted into the pipe body P, the caulking ring 2 is placed on the outer peripheral surface of the pipe body P and is compressed and deformed toward the nipple 1a, thereby fixing and connecting together the nipple 1a and pipe body P. Then, the pipe body P is deformed by the caulking ring 2a and is thereby reduced in diameter. The inner wall surface of the pipe body P is filled into the recessed portions of the annular projections 13a formed on the outer surface of the inserting portion 11a of the nipple 1a, whereby, the connecting portion between the nipple 1a and pipe body P can be made airtight. Further, even in case where there is applied to the nipple 1a a force to pull out the pipe body P from the nipple 1a, the pipe body P is caught by the annular projections 13a to compete with the pull-out force and thus the pipe body P can be prevented against removal.
However, in the above-mentioned spiral pipe joint of the related art, in case where the pipe body P of the spiral pipe is small in thickness, due to the step level difference between the projected and recessed portions of the annular projections, the inner surface of the spiral pipe is easy to break. In case where the caulking force by the caulking ring 2a is weakened in order to avoid such breakage of the spiral pipe inner surface, the spiral pipe can be removed from the nipple 1a. That is, in the above-mentioned spiral pipe joint in the related art, there is still left a problem that it is very difficult to eliminate both of the spiral pipe inner surface breakage and spiral pipe slippage at the same time by adjusting the caulking force.
The present invention aims at eliminating the above drawbacks found in the spiral pipe joint of the related art. Accordingly, it is an object of the invention to provide a joint for a spiral pipe which can simplify the structure of a joint main body, does not need to change the operation to mount itself onto a spiral pipe, and can not only prevent the inner surface of the spiral pipe against breakage but also prevent the spiral pipe against removal. It is another object of the invention to provide a method of connecting a joint to a spiral pipe with an outer periphery of a pipe wall thereof formed in an uneven spiral shape.
Now, using reference characters used in an embodiment of the invention illustrated herein, description will be given below the structure of the invention, which is provided for attaining the above object. A joint for a spiral pipe with the outer periphery of the pipe wall thereof formed in an uneven spiral shape, according to the invention, comprises: a nipple 1 which is to be inserted into the end portion of a pipe body P and forms a main body of the joint; a caulking ring 2 for fixing the pipe body P to the nipple 1; and, a flexible string-shaped pressure contact member 3 which is to be fitted into a spiral groove formed in the outer peripheral surface of the pipe P. The nipple 1 is formed of metal in a cylindrical shape; and, it includes a flange portion 12 formed in one end portion thereof, an inserting portion 11 to be inserted into the pipe body P, and a small-diameter stepped portion 13 formed in the inserting portion 11 on the flange portion 12 side thereof. The caulking ring 2 is formed of metal in a cylindrical shape having such an inside diameter that allows the caulking ring 2 to be fitted with the outer peripheral surface of the pipe body P. In the present joint, after the inserting portion 11 of the nipple 1 is inserted into the pipe body P, the pressure contact member 3 is wound once or more times around the outer peripheral surface of the portion of the pipe body P that exists above the inserting portion 11, and the caulking ring 2 is placed on the outside of the thus wound pressure contact member 3 in a radial direction of the pipe body P and is compressed in the center direction of the pipe body P to thereby reduce the diameter of the caulking ring 2 in such a manner that the caulking amount thereof on the small-diameter stepped portion 13 is larger than the step level difference between the inserting portion 11 and small-diameter stepped portion 13, whereby the nipple 1 and pipe body P can be fixed and connected to each other.